1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and a method for use in abandonment of oil and gas wells. More particularly, embodiments of the invention relate to removal of well tubulars using a clamp for use with a cutting system on an offshore platform.
2. Description of the Related Art
After a well has depleted its particular pay zone of oil and/or gas, the well will typically be decommissioned. Decommissioning includes a number of activities, all designed to ensure the used well does not create environmental and safety concerns after its useful life is over. For example, lined wellbores extending into the earth are typically plugged with cement at various locations along their length to prevent the migration of remaining hydrocarbons to the surface where they could escape into the environment. In addition to plugging activities, equipment at or near the surface must be securely removed, and this is especially important for equipment related to offshore wells.
Offshore platforms, formed from a combination of steel and concrete, include legs that extend to and into the seabed. These immobile structures are designed to help drill the wells and typically remain in place over producing wells to facilitate the gathering of oil and gas. When the well's production is complete, the platforms are moved to another location or disassembled.
In addition to the platforms themselves, strings of tubulars extend from the platform floor down to the seabed providing a communication path for oil and gas from the subsea wellbore to the platform. In some cases, a single platform serves a number of subsea wellbores, each with its own tubular string extending upwards to the platform floor. When a well is decommissioned, these tubulars extending from the wellbore must also be removed, typically by severing them at some depth below the seabed. Each string of tubulars can include multiple strings of differing diameters, each housed within the next with an annular area formed therebetween. A conductor is usually the largest diameter tubular in a well, and its purpose is to prevent the soft formations near the surface from caving in and to conduct drilling mud from the bottom of the hole to the surface when drilling starts. Smaller tubular strings within the conductor include casing and production tubing. These smaller diameter strings can also extend to the platform and need removal. In some instances smaller tubulars are grouted, or cemented in the larger conductor string whereby the annuli is filled with cement-like substances. In other instances the tubular strings within the conductor are not grouted and are therefore independent of each other.
Tubular removal can be carried out with mechanical or abrasive tools and methods. Mechanical cutting devices include cutters or knives disposed on a tool that is run into the tubular string on a work string to a depth where cutting is to take place. The tool is actuated, usually by rotation, and a wall of the tubular is destroyed as the cutters separate the tubular into an upper and a lower portion. Thereafter the tool is removed and the severed portion of tubular string is pulled up to the platform or a vessel, usually with the help of a crane or some type of jack.
Other cutting means include abrasive water jet cutting. An abrasive water jet cutter is also operated from inside a tubular string and severs the tubular by penetrating the wall with high-energy, high-velocity abrasive-filled water. Abrasive water jet cutters are especially effective for cutting multiple strings of tubulars in one operation, like successively smaller strings within a conductor. U.S. Pat. No. 7,178,598 entitled “Device for a Hydraulic Cutting Tool” and assigned to the assignee of the present invention, describes a method and apparatus for severing or cutting a tubular at a location below the seabed, and that patent is incorporated herein in its entirety.
Unlike mechanical cutting, abrasive water jet cutting produces a very “clean” cut, removing very little material from the tubular wall as the cut is made. Because so little material is removed, there is very little movement of the tubular string at the surface and often no way to be certain that the cut has been completed and the tubular severed. For this reason, abrasive water jet cuts are “proven” by lifting the upper portion of the tubular at least several inches to demonstrate its readiness for hoisting to the platform floor. To quickly and easily prove the cut, a typical jet cutting assembly includes a pair of cylinders that pull upwards on the tubular after the cut is made. If the tubular has been successfully cut, the upper portion will move upwards to prove the cut. If not, the cutting apparatus (which is still in tubular) is once again operated until the cut can be successfully proven. In the case of multiple tubular strings, an operator knows the cut is successful and all tubulars have been cut if the outer conductor is liftable. Once the cut has been proven, the cutting assembly is relocated to another conductor on the platform or to another job. A large-capacity crane, typically on a derrick barge, collects the severed strings for disposal.
One time-consuming aspect of proving abrasive water jet cuts on offshore tubulars involves the connection means needed between the lifting cylinders and an upper end of the tubular. Currently, lifting lugs are welded onto opposite sides of the tubular wall prior to the cutting operation to provide a lifting connection. The lifting lugs are necessary because without them there would be no way to effectively connect the tubular to the lifting cylinders so that its weight can be borne in the proving process. While the lifting lugs are effective, their installation requires time and a skilled worker's attendance on the platform and requires welding or other hot work that is considered a dangerous activity, even on a non-producing well. Further the welded lifting lugs are permanently installed, and their location on the tubular cannot be changed or adjusted in the event that the lugs are needed in a different rotational or axial location on the tubular.
Therefore, there is a need for a simple, flexible and cost-effective apparatus and method for making a temporary attachment to tubulars for proving an abrasive water jet cut.